Despite how badly he could've mangled them, the Green Lantern Corps should have obviously been his main point of interest for a string of movies. It has potential for a large ensemble cast and isn't being worked on like Batman, it is a close analogue to GotG in subject matter, and like Suicide Squad it had a poor-performing predecessor which he could come along and "fix" to further improve his reputation; even following the same format he always does would be more readily accepted for Green Lantern than it would for a character as incongruous to his ideas as Superman.